1. Field of the Invention
The present invention generally relates to an activating flux and, more particularly, to a welding activated flux for structural alloy steels.
2. Description of the Related Art
Structural alloy steel is a low alloy steel with carbon contents between 0.2% and 0.7%. Structural alloy steels contain various alloy elements such as nickel, chromium and molybdenum, improving the corrosion resistance, the mechanical strength at high temperature, the impact toughness at low temperature and the mass effect in quenching of steels. Nowadays, structural alloy steels are widely used in high-mechanical strength and high-impact toughness designs, such as buildings, bridges, motorcycle skeletons, turbine blades, shafts, crankshafts and high-tensile bolts; and therefore, the welding procedures and welding rods (or welding wires) should be adjusted according to the properties of structural alloy steels, avoiding fractures in the weld zone when the weldment is subjected to loads.
Tungsten inert gas (TIG) welding is one of the most popular processes for joining structural alloy steels because it produces a high-quality weld. The heat for TIG welding is generated by an electric arc maintained between a tungsten electrode and the workpiece to be joined. The tungsten electrode and molten metal are protected from atmospheric contamination by an envelope of inert gas (such as argon or helium) during heating and subsequent cooling. The welding arc melts the workpiece and a conventional welding rod (or a conventional welding wire) to form a welding pool. A weld is formed after the welding pool cools and solidifies, and a weldment is obtained. The chemical composition of the conventional welding rod (or the chemical composition of the conventional welding wire) should be used corresponding to the chemical composition of the workpiece to be joined, which is understood by a person having ordinary skill in the art. However, TIG welding process is an arc welding process with lower power density of the heat source, the welding pool thus formed is wide and shallow, resulting in insufficient depth of the weld and decreased mechanical strength of the weldments. Therefore, the TIG welding process is not suitable for joining the workpieces with thickness over 3 mm.
Referring to FIG. 1A, to join the workpieces with thickness over 3 mm by the TIG welding process, sides 91, 91′ of two workpieces 9, 9′ are first milled by a cutter “M” to form bevel faces 92, 92′, respectively. Referring to FIGS. 1B and 1C, a groove is formed at the butt joint of the bevel faces 92, 92′ of the workpieces 9, 9′ for carrying out the TIG welding process by using the conventional welding rod (or the conventional welding wire) “W” and the tungsten electrode “E.” A weld 93 is formed after welding. Formation of the bevel faces 12, 12′ increases the depth of the weld 93. However, formation of the bevel faces 12, 12′ also increases the width of the weld 93. In addition, the heat-affected zone (HAZ) formed by the welding heat source has a larger range due to the formation of the bevel faces 12, 12′; thereby increasing distortion of the weldments and decreasing the mechanical strength of the weldments. Moreover, formation of the bevel faces 12, 12′ also extends operation time and increases manufacturing costs including costs of labors, welding rods (or welding wires) and welding gases.
In light of this, it is necessary to provide a welding activated flux for structural alloy steels.